This invention relates to slip ring cooling devices for electrical rotary machines, and more particularly to slip ring cooling devices suitable for electrical rotary machines of large capacity such as turbine generators, water turbine generators, etc.
As well known, forced draft cooling is adopted widely for cooling a slip ring except for particular cases such as oil cooling or water cooling. As size of the electrical rotary machines increases these days, field magnet currents also increase and there is an increase in numbers of brushes to be mounted on one slip ring, resulting in the brushes being crowded. Under such a condition, passages for the draft are restrained by the crowded brushes so that all the brushes cannot be cooled uniformly and well enough. Under such a condition, frictional characteristics, of the brush and electric currents flowing there become unbalanced on account of the unbalanced brush temperature. As a result, partial, abnormal wear and sparks in the brushes are induced, which phenomena extend to the other normal brushes successively, which causes such a serious accident as the electrical rotary machine can not be operated.
In order to solve such a defect, in conventional machines of this kind, slip rings are cooled by using a plurality of heat pipes inserted therein for effecting the heat transfer in the axial direction, in addition to the forced draft cooling means. This device is disclosed in Japanese Laying-open of patent application No. 49-74308.
In this Japanese Laying-open of patent application No. 4,974,308, the forced draft cooling means is used for cooling a slip ring and brushes, and further in order to cool the slip ring, so-called heat pipes are employed. In this construction, the slip ring has a plurality of holes formed axially in the peripheral portion. In these holes, there are inserted a plurality of pipes sealingly enclosing condensed liquid which has a large evaporation latent heat, which are called the heat pipes. The heat pipes are fixed to the slip ring through end plates disposed on both the sides. Each of the heat pipes is provided with a plurality of annular heat discharging fins mounted on both heat pipe end portions projected from each of the end plates.
When the slip ring is rotated, heat generated by electric resistance and friction caused between the slip ring and the brushes is transferred to lower temperature portions. Namely, the condensed liquid is evaporated by the heat generated by the slip ring and the brushes to raise the pressure around the evaporating portions, as a result the vapor generated by the evaporation is transferred to both the cooled ends with the fins by the pressure difference between the evaporation portions and the cooled ends. The vapor is condensed there, and returned to the evaporation portions, thus the heat is transferred from the evaporation portions to the condensation portions, whereby, theoretically, the heat generated by the brushes and the slip ring is axially transferred to be dispersed effectively, and the heat balance is effected rapidly.
However, practically, since the pipes exist in the heat passages to extend from the heat generation portions to the condensed liquid, the heat transfer in the radial direction is not effected enough, so that the slip ring and the brushes are not cooled well enough. Therefore, in order to increase pressure difference in the heat passage, it is necessary to supply a large amount of a cooling gas to the fins or to make the fins larger. However, it would make the electrical rotary machine larger and its construction complicated, so that it is not practical.
Further it is known that instead of the heat pipes, the side walls of axial holes made axially in the peripheral portion of the slip ring are used for containing therein the condensed liquid, and outer pipes with fins are mounted on the side portions of the slip ring so as to align with the axes of the holes. The outer pipes have openings made in the ends for supplying the condensed liquid into the holes and discharging it out of the holes. The openings are sealed with plugs. In this construction, the heat generated by the brushes and the slip ring is conducted directly to the condensed liquid enclosed in the axial holes so that the heat is dispersed effectively, and it is an improvement that also makes the temperature uniform.
As material of the slip ring, high carbon steel which is great in mechanical strength and wear-resistance is used, but the material is corrosive. In the electrical rotary machines such as turbine generators which have a long life cycle, attention must be payed to corrosion in order to keep the reliability because the corrosion may occur at the portions which are subjected to high temperature and high stress. Therefore a corrosion-preventing agent is admitted in advance in the condensed liquid. In order to check the condensed liquid or exchange it, openings are provided. Usually the condensed liquid is checked or exchanged at the time of periodical check of the electrical rotary machine, done every 1 or 2 years at a fixed time.
In this case, there is a serious problem as for allotment of an amount of the condensed liquid to the individual pipe or hole. Namely, in an electrical rotary machine rotating at a high speed such as the turbine generator, even when the condensed liquid is alloted a little unequally to the closed chambers the unbalanced condensed liquid amount makes violent vibration, which causes a serious accident such as stopping the operation. Therefore, close attention is directed to even allotment of the condensed liquid to the individual closed chamber, but it is not easily worked out, particularly in case of the electrical rotary machine of large capacity provided with a plurality of the closed chambers. Further, in order to keep the closed chambers liquid-tight, the sealing construction is made complicated and large-sized because it is rotated at a high speed. Therefore, the parts of the closed chamber which are projected out of the side of the slip ring are bars to checking the brushes or exchanging operation of them and a danger to operators.